Cement-bound active substance

ABSTRACT

The invention relates to a novel cement-bound material with a mineral binding agent, a mineral filler and/or mineral aggregates. Said cement-bound material has a proportion of a mass hydrophobing agent comprised of stearates, siliconates, silanes or siloxanes ranging from 0.5 to 20 wt. % with regard to the weight of the mineral binding agent. The cement-bound material also has a proportion of a corrosion inhibitor, which is capable of migrating and which is comprised of nitrites, benzoates, amio alcohols or of sodium monofluorophosphates ranging from 01. to 20 kg per m3 of the active substance, and/or has a proportion of flexible fibers.

[0001] The invention relates to a cement-bound material according to thepreamble of claim 1 or claim 3.

[0002] Various examples show that the durability of reinforced concretestructures is substantially lower than was assumed during theirplanning. For this reason up to half the national expenditure in thefield of construction goes in industrial countries towards the repair ofexisting buildings. Even such repair measures often do not show thedesired durability. This is due to the fact that efficient materials andmaterial systems are still missing which give the desired durabilityboth to new buildings as well as the repair of existing buildings.

[0003] The occurring damage is mainly based on the following mechanisms:

[0004] 1. Cement-bound materials are brittle and are subjected todifferential shrinkage deformations after their production. These twophenomena lead to a complex inherent tension state and to the formationof cracks on the surface of the building component. These cracksfacilitate the access of substances which lead both to the destructionof the concrete (sulfate) as well as to corrosion of the armoring(chlorides from anti-freeze salts). The corrosion products comprise avolume which is up to three times larger, leading to the chipping off ofthe concrete and to the exposure of the steel armoring.

[0005] 2. Cement-bound materials are porous systems which absorbdamaging substances (sulfates, chlorides, acids) into the pore system attheir surface by capillary suction, diffusion and permeation.

[0006] 3. Conventional cement-bound materials (primarily concrete) needto be compacted after their introduction into a shuttering by means ofvibration machines in order to achieve a homogeneous structure. Thiswork process is often not performed with the required diligence, leadingto the consequence that the concrete is inhomogeneous and the absorptionof damaging substances is strongly increased locally.

[0007] There are measures and products that are capable of preventing orameliorating certain of the above damage mechanisms. For example, it isknown from EP-A-0 286 112 to add synthetic fibers as a reinforcement forcement mortar or concrete, which fibers consist of monofilaments with atensile strength of a maximum of 80 kg/mm². From U.S. Pat. No. 4,261,754a reinforcing fiber element is known which consists of orientedpolyolefins in order to reinforce a matrix material such as cement. Thefibers have a varying cross section in the longitudinal direction androughened surfaces from which fibrils project. In U.S. Pat. No.4,483,727 a method for producing bundles made of polyethylene fibers isdescribed which is used for reinforcing brittle material such as cement,concrete plaster of Paris or the like. From U.S. Pat. No. 4,968,561 asynthetic monofilament made of polyvinyl alcohol is known which is usedas a reinforcement for cement mortar or concrete. U.S. Pat. No.5,399,195 describes a method for producing a cement material whichreduces self-induced cracking. For this purpose synthetic fiber bundlesare added, which bundles consist of 10 to 10,000 filaments per bundle.The filaments substantially consist of polyolefins, polyolefinderivatives and a polyester. Moreover, so-called corrosion inhibitorsare known from U.S. Pat. No. 6,071,436 and U.S. Pat. No. 6,174,461.So-called waterproofing agents are known from U.S. Pat. Nos. 5,531,812and 6,139,622 which make the surfaces of the concrete water-repellent.For this purpose aqueous solutions made of alkoxyl silanes, organicsilanes and organic siloxane resins are used.

[0008] There are no efficient concepts for material systems which arecapable of preventing all damaging mechanisms and their causes to suchan extent that the durability can be increased several times over ascompared with currently used methods.

[0009] The present invention is now based on the object of providing acement-bound material which shows a considerably higher durability andis especially suitable for repairing existing buildings.

[0010] This object is achieved by a material with the features of claim1 or claim 3.

[0011] The material in accordance with the invention comes with themajor advantage that as a result of mass hydrophobing the penetration ofcontaminant-containing water is prevented and thus the durability ofrepairs is increased considerably. The armoring steel is retroactivelyprotected against corrosion by adding migration-capable corrosioninhibitors.

[0012] Further advantages of the invention follow from the dependentclaims and the description below in which the invention is explained incloser detail by reference to an embodiment shown in the schematicdrawings, wherein:

[0013]FIG. 1 shows a diagram on the opening of a crack under tensileload;

[0014]FIG. 2 shows a diagram for illustrating extensional strengtheningin comparison with crack opening;

[0015]FIG. 3 shows an illustration of the mass hydrophobing;

[0016]FIG. 4 shows a diagram on the penetration depth of chlorides;

[0017]FIG. 5 shows a schematic tunnel cross section, and

[0018]FIG. 6 shows three steps for repairing the damaged concrete.

[0019] The same reference numerals have been used for the same elementsin the figures. Any first-time explanations relate to all figures,unless expressly stated otherwise somewhere else.

[0020] As is generally known, concrete is made of a mineral bindingagent such as natural unslaked lime, pozzolan, natural or Portlandcement, one or several mineral fillers such as powdered mineral, fluedust and microsilicates, and/or of mineral aggregates such as sand orgravel. Water and cement is mixed at a ratio of 1:2 and thereafter themineral fillers and/or the mineral aggregates are added at a certainratio. The maximum elastic strain of said normal concrete under tensileload is at approx. 0.01%. The cement-bound materials of the system asdescribed herein consist of the known concrete mixtures with anadditional proportion of a mass hydrophobing agent comprised ofstearates, siliconates, silanes or siloxanes of between 0.5 and 20 wt. %with regard to the weight of the mineral binding agent or cement andwith an additional proportion of a corrosion inhibitor which is capableof migrating and which is comprised of nitrites, benzoates, aminoalcohols or of sodium monofluorophosphates ranging from 0.1 to 20 kg perm³ of the material. In addition it is possible to add flexible metallicfibers made of steel and/or non-metallic fibers made of polyolefins suchas highly crystalline polyethylene, polyvinyl alcohol or aramide, with aheight-width ratio of 10 to 1000, preferably 200 to 600, a tensilestrength of 0.8 to 4.0 GPa and a modulus of elasticity of 20 to 230 GPa,preferably higher than 25 GPa, with a share of 0.1 to 4.0 vol. %,preferably 0.5 to 3.0 vol. %, relating to the total volume. Moreover,lightweight aggregates such as styrofoam balls, micro hollow balls,cellular glass, swelling clay and the like can be added. Optionally, itis also possible to add further additives such as high-performanceliquefiers, shrinkage reduction agents, shrinkage compensation agents,stabilizers, air-entraining agents, retarding admixtures, hardeningaccelerators, defrothing agents, etc.

[0021]FIG. 1 shows the crack opening under deformation-controlledtensile load in various compositions of the cement-bound material. FIG.1a shows the crack opening in concrete without fiber reinforcement: at atension of approx. 3 N/mm² the material is locally weakened to such anextent that elongation weakening occurs and the cement-bound materialbreaks apart at a crack opening of approx. 2 mm. FIG. 1b shows the crackopening in a fiber-reinforced cement-bound material as is known from thestate of the art as described in the introduction. A large crack 10 isbridged here by fibers 11, so that a higher elongation capacity isachieved. In this case the strength decreases approximately linearly.FIG. 1c shows the crack opening in a cement-bound material according tothe present invention, with very small or so-called microcracks 13 beingproduced. For this purpose, variable shares of flexible metallic and/ornon-metallic fibers made of steel or polyolefins (highly crystallinepolyethylene, polvinyl alcohol, aramide) are added. The fiber volumeshare lies between 0.1 and 4.0%, preferably 0.5 to 3.0%, relating to thetotal volume, with a height-width ratio of 10 to 1000, preferably 200 to600, a tensile strength of 0.8 to 4.0 GPa and a modulus of elasticity of20 to 230 GPa, preferably higher than 25 Gpa. It has been noticed thatat a share of 0.1 to approx. 0.7 vol. % the behavior according to FIG.1b is still just about obtained. At a share of approx. 0.7 vol. % to 3.0vol. % the behavior according to FIG. 1c is obtained, however.

[0022]FIG. 2 shows the elongation strengthening of the cement-boundmaterial with microcracks. At a maximum elongation of approx. 8% theweakening commences, as a result of which larger cracks 14 are formedand the tension decreases in an approximately linear fashion in theconcrete.

[0023]FIG. 3 shows the penetration depth of chlorides in a concretewithout mass hydrophobing (FIG. 3a) and with mass hydrophobing (FIG.3b). The contaminated zone 20 can clearly be seen, which reaches up tothe armoring steel 21. The concrete component 22 which is situated belowthe armoring steel 21 is not further contaminated. When concrete has nowbeen applied with mass hydrophobing agents, the penetration depth of thechlorides is approximately zero, meaning that it is a few millimeters atmost. The respective diagram in FIG. 4 shows the measured penetrationdepth for the two materials. The measurements were performed after asurface contact during a period of 180 days with a 3% Cl⁻ solution. W/Zdesignates the ratio of water to cement, which has been inserted here asa standard of 1:2 for the measurements.

[0024]FIG. 5 schematically shows a tunnel cross section 25 with adamaged region 26. The following steps of FIGS. 6a through 6 c arenecessary for repairing this region.

[0025] For this purpose the cracked, contaminated covering concrete 26is removed up to the corroding armoring steel 21 (FIGS. 6a and 6 b).Usually, the concrete component 22 which is situated underneath is notcontaminated. Subsequently, the new, mass-hydrophobed cement-boundmaterial 27 is applied which in addition comprises corrosion inhibitors28 which are capable of migration, migrate through the concrete to thearmoring steel 21 and protect the same from further corrosion.

[0026] The components of the new cement-bound material have thefollowing effect on the damage mechanisms:

[0027] The effect of the fibers is on the one hand that they distributethe deformations occurring by the shrinkage in such a way over theentire surface that no cracks occur or only cracks that are opened soslightly that they do not cause any endangerment due to the absorptionof harmful substances. On the other hand, it is possible to entirelyomit the conventional steel armoring for certain applications as housingconstruction, which leads to the complete avoidance of damage bycorrosion. The behavior of the present cement-bound material is causedby the fact that the fibers bridge the microcracks caused by strain,prevent their further opening and transmit the mechanical strain toadjacent zones where also microcracks are produced, etc. As a result,only very small cracks are produced in the cement-bound material. As aresult of this phenomenon of the so-called multiple crack formation, theload-carrying and deformation capability is increased considerably ascompared with cement-bound materials without fibers.

[0028] Mass hydrophobing agents are substances on the basis ofstearates, siliconates, silanes or siloxanes which are added to thecement-bound material during its production and reduce the wetting angleof contact of the capillary pores of the hardened material to such ahigh extent. In this way, the absorption of liquids (and primarilycontaminant-containing water) is reduced to such a high extent that theeffects of the aforementioned damage mechanisms are prevented or atleast strongly ameliorated (cf. FIGS. 3 and 4). The proportion in weightof mass of hydrophobing is between 0.5 and 20 wt. % relating to theweight of the mineral binding agent.

[0029] Corrosion inhibitors are substances on the basis of nitrites,benzoates, amino alcohols or of sodium monofluorophosphates whosebipolar molecules lead to a passivation of the steel and thus to aprotection from corrosion when deposited on the armoring steel or onsteel fibers (inhibition of cathodic or anodic partial reaction). Theshare in weight is 0.1 to 20 kg per m³ of the cement-bound material (seeFIG. 6).

[0030] High-performance plasticizers are substances on the basis ofpolycarboxylates, melamines or naphtalene sulphonates and are added onthe one hand in order to reduce the water demand of the cement-boundmaterial, leading to a lower porosity and lower shrinkage deformations,which then leads to longer durability. On the other hand, they lead toself-compacting capabilities of the cement-bound material when added insufficient quantities and under predetermined conditions. Theself-compacting capability leads to the avoidance of structuralinhomogeneities due to improperly performed external compaction by meansof vibration equipment. The result is a highly homogeneous material. Thecontent of high-performance plasticizer is between 0.1 and 3% relatingto the binding agent mass. This means that vibration compacting can beomitted.

[0031] The variation of the components of the material allows settingthe consistency in such a way that it can be applied in many differentways, namely either mechanically or manually with the wet or dryspraying method, by hand, provided with a shuttering, vibrated orself-compacting, or on location at the construction site or in theproduction of assembly units (extruded).

[0032] Applications

[0033] The statical loads are low in housing construction. Concretestructures that are armored with armoring steel can accordingly bereplaced by fiber-reinforced cement-bound materials according to theabove explanation. Moreover, the consistency of the used material can beset to be self-compacting. As a result, the laying of steel armoring aswell as compacting by means of vibration equipment can be omitted.

[0034] When repairing the walls of a drift mining tunnel, the concretecover is removed up to the first corroded layer of armoring. Amass-hydrophobed cement-bound material is used for reproducing thesurface, which substance is provided with a fiber reinforcement andcontains a corrosion inhibitor which is capable of migration. Due to thefiber armoring the formation of cracks on the surface of the new layeris prevented. The corrosion inhibitors migrate into the existing baseand protect or re-passivate the steel armoring there from new or furthercorrosion. The mass hydrophobing prevents the penetration ofcontaminant-containing water. The durability of this repair is higher byseveral times than that of the original structure or that of any otherrepair measure (cf. FIG. 4).

[0035] In drift mining, jetcrete is frequently used for lining thetunnel cross section that has broken out. Frequently, it is equipped atfirst with steel armoring nets or steel fiber concrete is used. Analternative is using a mass-hydrophobed and fiber-reinforcedcement-bound material. The mass hydrophobing prevents the penetration ofaggressive (e.g. sulfate-containing) mountain water. The fibers assumestatical functions. This prevents any likelihood of steel corrosion andthe concrete is protected from damaging substances.

[0036] In certain applications, e.g. when conducting repairs accordingto FIG. 6 where after the removal of the damaged old concrete not onlyone but two layers of a new material are applied, it is possible to omitthe fibers in the new material for the first, lower layer and to providein addition only the mass hydrophobing and the corrosion inhibitor,since only the first upper layer is subjected to desiccation and thus tothe risk of crack formation. In the new material of said second, upperlayer on the other hand, it is possible to omit the corrosion inhibitorsand to provide additionally only the fibers and a mass hydrophobingagent.

1. A cement-bound material with a mineral binding agent, a mineralfiller and/or mineral aggregates, characterized in that there isprovided a proportion of a mass hydrophobing agent comprised ofstearates, siliconates, silanes or siloxanes ranging from 0.5 to 20 wt.% with regard to the weight of the mineral binding agent and aproportion of a corrosion inhibitor which is capable of migrating andwhich is comprised of nitrites, benzoates, amino alcohols or of sodiummonofluorophosphates ranging from 0.1 to 20 kg per m³ of the material.2. A material as claimed in claim 1, characterized in that a proportionof flexible fibers is provided with a with a height-width ratio of 10 to1000, preferably 200 to 600, a tensile strength of 0.8 to 4.0 GPa and amodulus of elasticity of 20 to 230 GPa, preferably higher than 25 GPa,with a share relating to the total volume of 0.1 to 4.0 vol. %,preferably 0.5 to 3.0 vol. %.
 3. A cement-bound material with a mineralbinding agent, a mineral filler and/or mineral aggregates, characterizedin that there is provided a proportion of a mass hydrophobing agentcomprised of stearates, siliconates, silanes or siloxanes ranging from0.5 to 20 wt. % with regard to the weight of the mineral binding agentand a proportion of flexible fibers with a height-width ratio of 10 to1000, preferably 200 to 600, a tensile strength of 0.8 to 4.0 GPa and amodulus of elasticity of 20 to 230 GPa, preferably higher than 25 GPa,with a share relating to the total volume of 0.1 to 4.0 vol. %,preferably 0.5 to 3.0 vol. %.
 4. A material as claimed in claim 2 or 3,characterized in that the flexible fibers consist of steel and/orpolyolefins, especially of highly crystalline polyethylene, polyvinylalcohol or aramide.
 5. A material as claimed in one of the claims 1 to4, characterized in that at least one lightweight aggregate such asstyrofoam balls, micro hollow balls, cellular glass or swelling clay isprovided.
 6. A material as claimed in one of the claims 1 to 5,characterized in that further additives are provided such ashigh-performance liquefiers, shrinkage reduction agents, shrinkagecompensation agents, stabilizers or air-entraining agents.